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I will answer directly because it seems the students writing to this prompt are all struggling with it.

First, in Act I, scene i, Romeo references love because he saw the results of the fight between the servants of the Montagues and the Capulets. It makes him sad (he was sad already). He goes into a series of oxymorons:

Here's much to do with hate, but more with love.Why, then, O brawling love! O loving hate!O any thing, of nothing first create!O heavy lightness! serious vanity!Mis-shapen chaos of well-seeming forms!Feather of lead, bright smoke, cold fire,sick health!Still-waking sleep, that is not what it is!This love feel I, that feel no love in this.

Shakespeare structures Romeo's speech as a series of opposites that have multiple layers of meaning while he is talking about the feuding families. What is so ironic about this passage is how it foreshadows what is to come. He is referring to that fight as something that is more about love than it is about hate and he hasn't even met Juliet yet. He has no idea how true his words are. And in the end, this "still-waking sleep" could foreshadow Juliet's seeming death that makes Romeo take his own life. After that point his will not feel love any more. Their family and their relationship is one big oxymoron.

By Act II, scene ii, Romeo is so taken with Juliet he welcomes death. In the first act, Romeo is sad talking about the terror of the families' feud. By the II:ii, Romeo is happy, and welcoming the threat of the Capulet's guards. The structure of his language turns more into metaphor and simile as opposed to oxymorons.